For point-to-multipoint services (also denoted as one-to-many services) over systems such as the Internet Protocol (IP) multicast, the IP Data Casting (IPDC) and the Multimedia Broadcast/Multicast Services (MBMS) as defined by the Third Generation Partnership Project (3GPP), file delivery such as for instance the download of multimedia files is an important service.
MBMS define a mechanism to deliver multimedia content to the mobiles (receivers) over a Point-to-Multipoint (PtM) bearer. Using a PtM bearer instead of multiple PtP bearers to deliver bandwidth-intensive multimedia content results in an efficient usage of available spectrum and other resources.
Feedback from the mobile could be useful for many purposes e.g., retransmission, rate adaptation and Delivery Verification (DV) etc. For PtP sessions, there already exist well-defined mechanisms to provide feedback and to utilize feedback for Quality of Service (QoS) improvement and charging.
However, for PtM connections, feedback from the mobiles could result in feedback implosion at the sender. Yet it is desirable to have at least some feedback from all the users participating in the PtM session:                Feedback from the mobiles with unsuccessful reception can be used to serve them over a PtP repair session that follows the original PtM session.        Feedback from the mobiles with successful reception can be used for charging purposes. This is termed as “Delivery Verification” in publication 3GPP TS 22.246: “MBMS User Services: Stage 1”, wherein section 5.3 of this publication defines general requirements for DV and Annex A of this publication provides some use cases for DV.        
DV reporting can be important for carriers for various reasons, that includes (but is not limited to), charging the customer for services rendered, market research surveys, QoS adaptation etc. Content delivery is done over a PtM bearer, but DV is usually done over PtP bearers.
PtP connections for DV reporting from thousands of mobiles to a small set of report servers could overload the system due to feedback implosion. Moreover, a mobile could have participated in multiple MBMS sessions during a certain period of time. Sending the DV reports separately for each MBMS session is inefficient.
For mobiles with unsatisfactory reception, PtP repair sessions need to be scheduled immediately after the MBMS session, whereas DV reports may be scheduled over a longer period of time.
PtP connections for both classes of users must be efficiently scheduled to balance the overall load on the system. An efficient and extensible format, appropriate scheduling and the protocol elements for DV reports that take into account the above concerns does not exist in the MBMS.
3GPP technical document S4-040270, “MBMS Content Delivery Reporting”, proposes to uses the same overload prevention mechanisms for scheduling both DV reports and PtP repair requests and to execute DV reporting schemes after PtP repair schemes. But DV reports do not scale in the same way as PtP repairs i.e., typically 5% of users may need PtP repairs whereas 100% of users may have to perform DV reporting. This approach thus can not be considered optimum.